A centrifugal clutch is a clutch that uses centrifugal force to connect two concentric shafts, with the driving shaft nested inside the driven shaft. It engages more at higher speeds.
The input of the clutch is connected to the engine crankshaft while the output may drive a shaft, chain, or belt. As engine revolutions per minute increase, weighted arms in the clutch swing outward and force the clutch to engage. The most common types have friction pads or shoes radially mounted that engage the inside of the rim of a housing. On the center shaft there are an assorted number of extension springs, which connect to a clutch shoe. When the central shaft spins fast enough, the springs extend causing the clutch shoes to engage the friction face. It can be compared to a drum brake in reverse. This type can be found on most home built karts, lawn and garden equipment, fuel-powered model cars and low power chainsaws. Another type used in racing karts has friction and clutch disks stacked together like a motorcycle clutch. The weighted arms force these disks together and engage the clutch.
When the engine reaches a certain speed, the clutch activates, working somewhat like a continuously variable transmission. As the load increases, the speed drops, disengaging the clutch, letting the speed rise again and reengaging the clutch. If tuned properly, the clutch will tend to keep the speed at or near the torque peak of the engine. This results in a fair bit of waste heat, but over a broad range of speeds it is much more useful than a direct drive in many applications.
Centrifugal clutches are often used in mopeds, underbones, lawn mowers, go-karts, chainsaws, mini bikes, and some paramotors and boats tokeep the internal combustion engine from stalling when the output shaft is slowed or stopped abruptly
disengage loads when starting and idling.
Thomas Fogarty, who is also credited with inventing the balloon catheter, is credited with inventing a centrifugal clutch in the 1940s although automobiles were already being manufactured with centrifugal clutches as early as 1936. There is also a design for an 'automatic clutch' (essentially the same device) in the 'Meccano Magazine' of June 1931. But centrifugal clutches were used in railway locomotives much earlier (before 1858), and referred to (in relation to electric motors) in a patent of 1899